This invention relates to a monotube suspension dampers for a vehicle suspension system that is preloaded by the vehicle suspension spring.
Monotube gas charge dampers are conventionally used in vehicle suspension systems. These devices include a tubular housing connected to a wheel end assembly and filled with damping fluid, a piston slidably mounted in the tubular housing, and a piston rod secured to the piston. The piston rod extends from the tubular housing and is connected to the vehicle body. As the vehicle upon which the damper is mounted is driven, the piston and piston rod move within the tube, displacing the damping fluid, to thereby absorb road shocks and vibrations. Displacement of the piston and piston rod within the tube requires that the volume within the tube be compensated during this normal movement of the piston to accommodate extension and retraction of the piston rod. Heretofore, compensation has been accomplished by providing a gas cap which is slidably mounted within the tube and which responds to a gas pressure charge within a gas accumulator to move the gas cap within the tube to thereby provide volumetric compensation for the movement of the piston and piston rod within the tube and to thereby prevent cavitation. The gas cap also accommodates thermal expansion of the fluid and fluid loss. The gas cap and accumulator required on prior art dampers increases the length of the damper, thereby complicating packaging and installation of the damper on the vehicle, and is difficult to manufacture because of the high pressure gas charging that is required. A typical prior art damper of this type is disclosed in U.S. Pat. No. 5,706,920.
According to the invention, the gas cap and the accumulator necessary on prior art monotube suspension dampers is eliminated. According to one embodiment of the invention, the seal cover, which closes the upper end of the tube and through which the piston rod extends, is made slidable with respect to the tube. The seal cover is preloaded by the vehicle suspension spring. Accordingly, the weight of the vehicle body is applied to preload the seal cover, thereby providing the preload necessary to prevent cavitation. According to another embodiment of the invention, the bottom ring of the damper is moveable axially with respect to the tube. The vehicle suspension spring is connected to the tube to provide the necessary preload. Accordingly, because the gas cap and the accumulator are eliminated, the present invention has the advantage of providing a damper having a smaller overall length. Manufacturing is simplified since assembly of the damper is easier (since the gas cap and accumulator do not have to be charged with gas). Because of the higher preload force, cavitation during normal operation of the damper is substantially reduced.